Cartridge fuse with outer casing and overload interrupting chamber formed by inner sub-casing

ABSTRACT

A cartridge fuse includes a main casing and a sub-casing inside the main casing. The sub-casing houses the overload current interrupting means of the fuse and does not contain a pulverulent arc-quenching filler. The space bounded by the inner surface of the main casing and the outer surface of the sub-casing is filled with a pulverulent arc-quenching filler embedding the major fault current interrupting means of the fuse. The sub-casing is closed at least at one end by a pair of discs having juxtaposed rectangular cut-outs and defining a straight narrow slit. The sub-casing, the overload current interrupting means therein and the pair of ribbon fuse link sections extending from both sides of the sub-casing form a self-contained and self-sustaining subassembly which can readily be handled in the process of manufacturing the fuse. The aforementioned ribbon fuse link sections are pre-bent at sharp angles and form jointly with the sub-casing and the parts therein a clip-on unit, i.e. a unit that can simply be clipped on to the main casing without any metalforming operation and without use of any tool.

United States Patent Kozacka [54] CARTRIDGE FUSE WITH OUTER [58] Fieldof Search ..337/l59, 162, 166, 185, 231, 337/237, 248, 251, 252, 253,254, 292, 247,

[56] References Cited UNITED STATES PATENTS 3,491,322 1/1970 Kozocka..337/166 x 3,483,501 12/1969 Kozocka ..337/l66 961,891 6/1910 016111..337/252 x 1,103,987 7/1914 Murray ..337/248 1,788,770 1/1931 La Mar..337/254 x [151 3,681,731 1451 Aug. 1, 1972 Primary Examiner-Bernard A.Gilheany Assistant Examiner-Dewitt M. Morgan Attorney-Erwin SalzerABSTRACT A cartridge fuse includes a main casing and a sub-casing insidethe main casing. The sub-casing houses the overload current interruptingmeans of the fuse and does not contain a pulverulent arc-quenchingfiller. The space bounded by the inner surface of the main casing andthe outer surface of the sub-casing is filled with a pulverulentarc-quenching filler embedding the major fault current interruptingmeans of the fuse. The sub-casing is closed at least at one end by apair of discs having juxtaposed rectangular cut-outs and defining astraight narrow slit. The sub-casing, the overload current interruptingmeans therein and the pair of ribbon fuse link sections extending fromboth sides of the sub-casing form a self-contained and selfsustainingsub-assembly which can readily be handled in the process ofmanufacturing the fuse. The aforementioned ribbon fuse link sections arepre-bent at sharp angles and form jointly with the sub-casing and theparts therein a clip-on unit, i.e. a unit that can simply be clipped onto the main casing without any metal-forming operation and without useof any tool.

6 Claim. 5 Drawing Figures PATENTED M13 1 3.681. 731

FIG.I

l2 0 FREDERICK J. KOZACKA BY WWW ATTY.

BACKGROUND OF THE INVENTION There is a number of instances where it isnecessary to immerse some of the fusible means of an electric cartridgefuse in a pulverulent arc-quenching filler, and to keep the pulverulentarc-quenching filler away from other fusible means of the cartridgefuse. A so-called dual element fuse includes a fusible overloadinterrupting device and separate means for interrupting major faultcurrents. It is desirable to immerse the ribbon fuse links forinterrupting major fault currents in a pulverulent arc-quenching fillercapable of absorbing large amounts of energy, such as quartz sand, andto keep the pulverulent arc-quenching filler, in particular quartz sand,away from the break or breaks formed for interrupting overload currentsof inadmissible duration. In such instances a cartridge fuse may includea cylindrical main casing of electric insulating material and acylindrical sub-casing having a smaller outer diameter than the innerdiameter of the main casing, arranged inside of the main casing inspaced relation from the lateral wall thereof. The sub-casing is closedat its ends but has means for the passage of current-carrying conductorsthrough it. The space bounded by the main casing is filled with apulverulent arc-quenching filler, except that occupied by thesub-casing, i.e. the latter defines a void or empty space for theoverload current interrupting means.

Where the interrupting duty of a fuse is not severe a tubular sub-casingmay be made of a tubular material capable of being squashed and thusclosed. Dual element fuses having sub-casings of this description aredisclosed in US. Pat. No. 3,483,501 to Frederick J. Kozacka, Dec. 9,1969 for Electric Cartridge Fuse. In cases where the interrupting dutyis relatively severe the sub-casing ought to be made of a relativelystiff material that does not lend itself to squashing. Nor can thesquashing technique shown in the above patent be adopted in instanceswhere the reduction of the internal volume of the sub-casing inherent inthe sub-casinG squashing technique is not desirable, or not acceptable.In some instances it is possible to close one or both ends of asub-casing by a circular cover disc having an aperture or slit thereinfor the passage of ribbon conductor means through the cover disc, theaperture or slit fitting the ribbon conductor means sufficiently closeto preclude penetration of the pulverulent arcquenching filler from thespace outside the sub-casing into the sub-casing. Closing of asub-casing by an apertured disc or washer becomes difficult if and whenit is desired to have pre-bends in the conductor or conductors extendingthrough one or both end surfaces of a sub-casing.

This invention refers to an improvement of the structure shown in theabove referred to US. Pat. No. 3,483,501. This improvement consists, inessence, in imparting such a configuration to the overload interruptingmeans and to the major fault current interrupting means that theyjointly form a clip-on unit that can simply be clipped on to the maincasing without resorting to any tool, or tools. The structure includesprebent fusible conductors, a non-squashed sub-casing and cover meanswhich make it possible to conveniently close a sub-casing irrespectiveof the configuration of the portion of the conductor means or ribbonfuse link which is situated outside of the sub-casing.

SUMMARY OF THE INVENTION In fuses according to the present invention atleast one end of a cylindrical sub-casing is closed by a pair ofcircular discs having substantially the same diameter as the sub-casingand having juxtaposed rectangular cutouts. Said pair of discs isarranged at right angles to the axis of the sub-casing and in abuttingrelation to the latter. The discs define between the cut-outs thereof astraight narrow slit for the passage of one of a pair of ribbon fuselink sections from the outside of the subcasing into the inside thereof.The aforementioned ribbon fuse link sections are pre-bent in such afashion that they form jointly with the sub-casing a substantiallyC-shaped self-contained and self-supporting clipon assembly unit, i.e. aunit which can be clipped on, or fastened to, the main casing withoutmetal-forming and without resorting to any tool, or tools.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is partly a side elevation of afuse embodying this invention and partly a longitudinal section of sucha fuse taken substantially along H of FIG. 2;

FIG. 2 is in substance a top plan view of the structure of FIG. 1showing the end surface of the terminal cap as being partly broken awayand the lateral surface of the terminal tap sectioned by a horizontalplane;

FIG. 3 is a side elevation of the top end of the structure of FIG. 1 asseen from right to left;

FIG. 4 is an exploded top-plan view of a detail of the structure of FIG.1; and

FIG. 5 is a portion of FIG. 1 drawn on a larger scale than FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENT Referring now to the drawings,numeral 1 has been applied to indicate a tubular main casing of electricinsulating material, e.g. fiber or glass-cloth melamine. Casing l isclosed on the ends thereof by terminal caps or ferrules 2, each providedwith a knife blade contact 2a. The axially inner edges 3 or terminalcaps 2 are crimped into casing l. Sub-casing 4 is arranged inside ofmain casing l in coaxial relation to the latter. The outer diameter ofsub-casing 4 is substantially less than the inner diameter of maincasing 1. Therefore a toroidal gap is formed between main casing l andsubcasing 4. The upper portion of sub-casing 4 is provided with a liner4' of insulating material forming an upper shoulder 4". A like shoulderis formed by liner 4' substantially midway between the ends ofsub-casing 4. The sub-housing 4 houses two spring-biased parts 6'and 7of which the former is substantially in the shape of a plunger and thelatter substantially in the shape of a bell, or inverted pot. The upperend surface of part 7 forms an annular flange, and helical spring 8rests with the upper end thereof against that flange. The lower end ofhelical spring 8 rests against a flange integral with plunger 6 insideof bell-shaped member 7. Member 7 is also provided with a radiallyoutwardly projecting flange 7a abutting against the lower rim orcircular edge of sub-housing 4. The bottom of member 7 is closed by adisc-shaped cover plate 13 of metal and the axially inner end of fusibleelement or ribbon fuse link 9" is soldered at 7' to cover plate 13 by asoft solder having a relatively high fusing point. Reference character6' has been applied to indicate two solder joints formed by soft solderhaving a relatively low fusing point. One of these two solder jointsconductively interconnects parts 6 and 7, and the other of these twosolder joints conductively interconnects plunger 6 and the axially innerend of a fusible element or ribbon fuse link 9'. Fusible elementsections 9 and 9" are perforated copper ribbons as clearly shown in FIG.3 wherein reference character 14 has been applied to indicateperforations in fusible element or fuse link 9.

The upper end of sub-housing 4 is closed by a pair of circular discs5a,5b of electric insulating material of which the lower disc 5b restsagainst shoulder 4" and the upper disc 5a rests upon lower disc 5b. Asseen in FIG. 4 the juxtaposed sides of discs 5a,5b are provided withrectangular cut-outs. When discs 5a,5b are superimposed in registrythese rectangular cut-outs define a narrow slit allowing the passage offuse link section 9' from the space within sub-casing 4 to the spaceoutside sub-casing 4 and within main casing 1.

The ends of fuse link sections 9',9" immediately adjacent sub-casing 4extend along the axis of main casing 1. Each fusible element section9',9" has a first bend inside of main casing 1 and a second bendcoextensive with one of the rims of main casing 1. The axially outerends of fusible element means 9',9" are sandwiched between the outersurface of easing l and the radially inner surfaces of caps 2. Each ofcaps 2 has a circular aperture 2c in the lateral surface thereofarranged opposite to, or in registry with, one of the ends of fusibleelement means 9',9". A solder joint 11 is arranged inside each of thecircular apertures 2c in caps 2, each solder joint 11 conductivelyconnecting the axially outer end of one of fuse links 9',9" to one ofterminal caps 2. The radially outer surface of each solder joint 11 iscovered with a heat resistant protective layer 12 to avoid exposurethereof to the effects of ambient atmospheres. Protective layer 12 maybe formed by silicone grease.

Sub-casing 4 is surrounded by a body of pulverulent arc-quenching fillerl embedding fusible element section 9,9" filling main casing 1. Discs5a,5b preclude arc-quenching filler from penetrating into sub-casing 4where its presence is not desired. Discs 5a,5b may be held in positionby friction. Upon filling main casing 1 with filler 10 the latter tendsto maintain discs 5a,5b in proper position.

0n occurrence of protracted overloads solder joints 6 soften and plunger6 moves under the action of spring 8 away from the axially inner end offusible element 9. Thus an arc is kindled which is confined to a chamberformed by sub-casing 4. This chamber does nOt contain any pulverulentarc-quenching filler whose properties are not compatible with theinterrupting requirements for low current arcs. Thus parts 4,4, 5a,5b,6,7,8 and 13 form an effective overload interrupting device.

The ribbon fuse link sections 9, 9" are a means for interrupting majorfault currents, such as short-circuit currents.

ribbon fuse link section 9,9" must be sufiiciently stiff I to retainwithout support any shape imparted to them, and more particularly theshape shown in FIG. 1. It is apparent from FIG. 1 that each fuse linksection 9,9" includes an inner end and an outer end both parallel to theaxis of main casing 1. The intermediate portions of fuse link sections9,9" are diverging radially outwardly and the aforementionedsub-assembly forms a clip-on unit that can readily be affixed to casing1, thus greatly reducing the cost of, and the amount of time involvedin, production of the fuse.

When assembling the fuse shown in FIG. 1 the aforementioned clip-on unitis first inserted into the main casing 1. It has substantially the sameconfiguration prior to its insertion into main casing 1 as thereafter,i.e. each fuse link section 9,9" is pre-bent at two points prior toinsertion of the subassembly or clip-on unit into main casing 1. Eachfuse link section 9,9" has a first bend co-extensive with one point ofthe axis of sub-casing 4 and a second bend situated at a point having aradial spacing from said axis substantially equal to the radius of maincasing l. The aforementioned second bend of each fuse link section 9',9"is clamped between one rim of casing l and one end surface 2b of one ofthe terminal caps of ferrules 2. The axial spacing of said first bend offuse link sections 9',9" is substantially less than the length ofeasing 1. The axial spacing of the second bend of ribbon fuse linksections 9',9" are sufficiently equal to the length of casing l. Fuselink sections 9,9" are sufiiciently stiff to retain the shape thereofwithout any support other than the support provided by parts 6 and 7 andsub-casing 4. On the other hand, the fuse link sections 9,9" arerelatively resilient to make it possible to be bent from right to left(as seen in FIG. 1) and then snap into place, i.e. the position shown inFIG. 1. Upon having inserted the snap-on unit 9',6,7,8,5a,5b,4,4',13 and9" into main casing 1 one terminal cap 2 is mounted in place andthereupon the pulverulent arc-quenching filler 10 is filled intocasing 1. Then the other terminal cap 2 is mounted on main casing 1 andthe two solder joints 1] are formed.

Finally the protective silicone grease layers are placed into theapertures 20 of caps 2.

I claim as my invention:

1. A sub-assembly for making time-lag fuses includa. a cylindricaloverload interrupting device casing;

b. a fusible overload interrupting device including a spring-biasedswitching means and a soft solder element normally maintaining saidswitching means in the closed position thereof arranged inside saidcasing;

. means for closing the end surfaces of said casing;

. a pair of ribbon fuse link sections for interrupting major faultcurrents connected in series with said overload interrupting device eachprojecting away from one of the end surfaces of said casing, said ribbonfuse link means being sufficiently stiff to retain without support theshape imparted to them, each of said ribbon fuse link sections beingprebent and having an inner straight end substantially parallel to theaxis of said casing, an outer straight end substantially parallel tosaid axis of said casing and an intermediate straight portion inclinedto said axis of said casing, said pair of fuse link sections beingsufficiently resilient to snap back to the position thereof upon havingundergone limited transverse bending, and said pair of fuse linksections and said casing jointly forming a substantially C-shapedself-contained and self-supporting clipon unit adapted to be clipped inposition inside of a fuse casing.

2. A sub-assembly as specified in claim 1 wherein at least one end ofsaid casing is closed by a pair of circular discs of insulating materialhaving substantially the same diameter as said casing and superimposedin registry, each of said pair of discs having a substantiallyrectangular cut-out and the cut-out of said pair of discs defining astraight narrow slit for the passage of one of said pair of ribbon fuselink sections.

3. A sub-assembly for making time-lag fuses includmg I a. a cylindricaloverload interrupting device casing;

b. a fusible overload interrupting device inside said casing, saidoverload interrupting device including a switch means spring-biased tothe open position thereof and a solder joint normally maintaining saidswitch means in the closed position thereof;

c. means for closing the end surfaces of said casing;

d. a pair of ribbon fuse link sections for interrupting major faultcurrents connected in series with said overload interrupting device eachprojecting away from said overload interrupting device in a directionsubstantially longitudinally of said casing, said ribbon fuse linksections being sufficiently stiff to retain without support a shapeimparted to them, each of said ribbon fuse link sections being pre-bentand including a substantially straight inner end conductively connectedto said overload interrupting device, a substantially straight radiallyouter end substantially parallel to said axis of said casing and anintermediate substantially straight portion inclined to said axis ofsaid casing, said pair of fuse link sections being sufficientlyresilient to snap back to the initial position thereof upon havingundergone some transverse bending out of said position, and said pair offuse link sections and said casing jointly forming a self-contained andself-supporting clip-on unit adapted to be clipped in position inside afuse casing.

4. A sub-assembly as specified in claim 3 wherein said housing is closedon one of the cylindrical ends thereof by a metallic cover plate towhich Said radially inner end of one of said pair of fuse link sectionsis soldered, and wherein said housing is closed on the other of thecylindrical ends thereof by a pair of circular discs havingsubstantially the same diameter as said casing and having juxtaposedrectangular cut-outs forming therebetween a narrow slit for the passageof one of said pair of ribbon fuse link sections from the outside ofsaid casing to the inside thereof.

5. An electric cartridge fuse including a. a cylindrical main casing ofelectric insulating material;

b. a pair of terminal caps mounted upon the ends of said main casing andclosing the ends thereof;

c. a cylindrical sub-casing having a smaller outer diameter than theinner diameter of said main casing arranged inside said main casing inspaced relation from the lateral wall thereof;

d. a fusible overload interrupting device inside said sub-casing, saidoverload interrupting device including a pair of relatively movablespringbiased parts normally restrained in position by solder jointmeans;

e. a pair of ribbon fuse link sections for interrupting major faultcurrents each having an axially outer end conductively connected to oneof said pair of terminal caps and an axially inner end conductivelyconnected to one of said pair of relatively movable parts, each of saidpair of ribbon fuse link sections being pre-bent at two distinct pointsincluding a first bend coextensive with one point of the axis of saidsub-casing and a second bend situated at a point having a radial spacingfrom said axis substantially equal to the radius of said main casing,the axial spacing of said first bend of said pair of fuse link sectionsbeing less than the length of said main casing and the axial spacing ofsaid second bend of said pair of fuse link sections being substantiallyequal to the length of 'said main casing, said pair of ribbon fuse linksections being sufficiently stiff to retain the shape thereof withoutany support other than the support provided by said pair of relativelymovable spring-biased parts and said sub-casing, said pair of ribbonfuse link sections being sufficiently resilient to snap back to theirinitial positions following a limited transverse bending thereof, andsaid pair of relatively movable spring-biased biased parts, saidsub-casing and said pair of ribbon fuse link section jointly forming asubstantially C-shaped self-contained and selfsupporting clip-onsub-assembly unit;

f. a body of pulverulent arc-quenching filler inside said main casingsurrounding said sub-casing and embedding said pair of fuse linksections; and

f. means for precluding said arc-quenching filler from entering intosaid sub-casing, said means including a pair of circular discs haVingsubstantially the same diameter as said sub-casing and having juxtaposedsubstantially retangulat cut-outs, said pair of discs being arranged atright angles to the axis of said sub-casing in abutting relation to saidsub-casing and defining between said cut-outs thereof a straight narrowslit for the passage of one of said pair of ribbon fuse link sectionsfrom the outside of said sub-casing into the inside thereof.

6. An electric cartridge fuse as specified in claim 1 wherein a. saidsub-casing includes an internal liner having a shorter length than saidsub-casing and forming a first shoulder adjacent one end of saidsub-casing and forming a second shoulder substantially midway betweenthe ends of said sub-casing; wherein b. said pair of circular discsabuts against said first shoulder; and wherein 0. one of said pair ofrelatively movable spring-biased parts is formed by a hollow cylinderabutting with one of the end surfaces thereof against said secondshoulder.

1. A sub-assembly for making time-lag fuses including a. a cylindricaloverload interrupting device casing; b. a fusible overload interruptingdevice including a springbiased switching means and a soft solderelement normally maintaining said switching means in the closed positionthereof arranged inside said casing; c. means for closing the endsurfaces of said casing; d. a pair of ribbon fuse link sections forinterrupting major fault currents connected in series with said overloadinterrupting device each projecting away from one of the end surfaces ofsaid casing, said ribbon fuse link means being sufficiently stiff toretain without support the shape imparted to them, each of said ribbonfuse link sections being pre-bent and having an inner straight endsubstantially parallel to the axis of said casing, an outer straight endsubstantially parallel to said axis of said casing and an intermediatestraight portion inclined to said axis of said casing, said pair of fuselink sections being sufficiently resilient to snap back to the positionthereof upon having undergone limited transverse bending, and said pairof fuse link sections and said casing jointly forming a substantiallyC-shaped selfcontainEd and self-supporting clip-on unit adapted to beclipped in position inside of a fuse casing.
 2. A sub-assembly asspecified in claim 1 wherein at least one end of said casing is closedby a pair of circular discs of insulating material having substantiallythe same diameter as said casing and superimposed in registry, each ofsaid pair of discs having a substantially rectangular cut-out and thecut-out of said pair of discs defining a straight narrow slit for thepassage of one of said pair of ribbon fuse link sections.
 3. Asub-assembly for making time-lag fuses including a. a cylindricaloverload interrupting device casing; b. a fusible overload interruptingdevice inside said casing, said overload interrupting device including aswitch means spring-biased to the open position thereof and a solderjoint normally maintaining said switch means in the closed positionthereof; c. means for closing the end surfaces of said casing; d. a pairof ribbon fuse link sections for interrupting major fault currentsconnected in series with said overload interrupting device eachprojecting away from said overload interrupting device in a directionsubstantially longitudinally of said casing, said ribbon fuse linksections being sufficiently stiff to retain without support a shapeimparted to them, each of said ribbon fuse link sections being pre-bentand including a substantially straight inner end conductively connectedto said overload interrupting device, a substantially straight radiallyouter end substantially parallel to said axis of said casing and anintermediate substantially straight portion inclined to said axis ofsaid casing, said pair of fuse link sections being sufficientlyresilient to snap back to the initial position thereof upon havingundergone some transverse bending out of said position, and said pair offuse link sections and said casing jointly forming a self-contained andself-supporting clip-on unit adapted to be clipped in position inside afuse casing.
 4. A sub-assembly as specified in claim 3 wherein saidhousing is closed on one of the cylindrical ends thereof by a metalliccover plate to which Said radially inner end of one of said pair of fuselink sections is soldered, and wherein said housing is closed on theother of the cylindrical ends thereof by a pair of circular discs havingsubstantially the same diameter as said casing and having juxtaposedrectangular cut-outs forming therebetween a narrow slit for the passageof one of said pair of ribbon fuse link sections from the outside ofsaid casing to the inside thereof.
 5. An electric cartridge fuseincluding a. a cylindrical main casing of electric insulating material;b. a pair of terminal caps mounted upon the ends of said main casing andclosing the ends thereof; c. a cylindrical sub-casing having a smallerouter diameter than the inner diameter of said main casing arrangedinside said main casing in spaced relation from the lateral wallthereof; d. a fusible overload interrupting device inside saidsub-casing, said overload interrupting device including a pair ofrelatively movable spring- biased parts normally restrained in positionby solder joint means; e. a pair of ribbon fuse link sections forinterrupting major fault currents each having an axially outer endconductively connected to one of said pair of terminal caps and anaxially inner end conductively connected to one of said pair ofrelatively movable parts, each of said pair of ribbon fuse link sectionsbeing pre-bent at two distinct points including a first bend coextensivewith one point of the axis of said sub-casing and a second bend situatedat a point having a radial spacing from said axis substantially equal tothe radius of said main casing, the axial spacing of said first bend ofsaid pair of fuse link sections being less than the length of said maincasing and the axial spacing of said second bend of said pair of fuselink sections being substantially equal to the length of sAid maincasing, said pair of ribbon fuse link sections being sufficiently stiffto retain the shape thereof without any support other than the supportprovided by said pair of relatively movable spring-biased parts and saidsub-casing, said pair of ribbon fuse link sections being sufficientlyresilient to snap back to their initial positions following a limitedtransverse bending thereof, and said pair of relatively movablespring-biased biased parts, said sub-casing and said pair of ribbon fuselink section jointly forming a substantially C-shaped self-contained andself-supporting clip-on sub-assembly unit; f. a body of pulverulentarc-quenching filler inside said main casing surrounding said sub-casingand embedding said pair of fuse link sections; and f. means forprecluding said arc-quenching filler from entering into said sub-casing,said means including a pair of circular discs haVing substantially thesame diameter as said sub-casing and having juxtaposed substantiallyretangulat cut-outs, said pair of discs being arranged at right anglesto the axis of said sub-casing in abutting relation to said sub-casingand defining between said cut-outs thereof a straight narrow slit forthe passage of one of said pair of ribbon fuse link sections from theoutside of said sub-casing into the inside thereof.
 6. An electriccartridge fuse as specified in claim 1 wherein a. said sub-casingincludes an internal liner having a shorter length than said sub-casingand forming a first shoulder adjacent one end of said sub-casing andforming a second shoulder substantially midway between the ends of saidsub-casing; wherein b. said pair of circular discs abuts against saidfirst shoulder; and wherein c. one of said pair of relatively movablespring-biased parts is formed by a hollow cylinder abutting with one ofthe end surfaces thereof against said second shoulder.